Photoacoustic measurements of single red blood cells

A photoacoustic method to infer the size, shape and orientation of single RBCs is presented. Diseased or damaged RBCs frequently have abnormal shapes and sizes, which can result from a variety of diseases. When using frequencies between 100 and 500 MHz, the photoacoustic power spectrum from RBCs has periodically varying minima and maxima that depend on the size and shape of the RBC. The signals from RBCs in a vertical and horizontal orientation relative to the transducer were compared to numerical simulations using a finite element model. Three different shapes commonly used to model RBCs were examined (at constant volume): a biconcave disk, an oblate ellipsoid and a sphere. For a single biconcave shaped RBC, good agreement in the shape of the power spectrum was observed between measured and numerical simulations for the RBC in both the vertical and horizontal orientation relative to the transducer. When the RBC was placed in a hypotonic solution, it swelled to a spherical shape. In this case, good agreement was observed between the measured signal and the spherical model. In this paper, we show that the photoacoustic power spectrum can be used to infer the size, shape and orientation of single RBCs.